272 THE STRUCTURE AND LIFE OF BIRDS CHAP. 
have somehow to account for what seems to be a well- 
established fact—viz., that the American Golden Plover 
as it travels southward in autumn accomplishes over 
1,700 miles in one flight. Even if we assume an 
average rate of sixty miles per hour, the birds would 
be over twenty-eight hours on the wing, and this is a 
long time to be without food. 
Further experiments on the velocity of the flight of 
birds of different species under varying conditions are 
much to be desired. 
A pace of over 30 miles per hour is maintained by 
race-horses over a short course. Ladas’ time over the 
Derby course, 14 miles, gives him a velocity of 324. 
A Note on Flying Machines. 
It is difficult in writing of flight to leave unmen- 
tioned the subject of flying machines. At the same 
time, an elaborate account of them would be out of 
place here. Not many years back it was supposed that 
only in balloons was aerial navigation possible for 
men, and the problem that was for ever being debated 
was, How is it possible to steer a balloon? With a 
vehicle that travels with the air and has no velocity of 
its own, steering is practically an impossibility. Since 
this has been realised, attention has been diverted 
from balloons to flying-machines, which are, necessarily, 
heavier than the surrounding air, since, if they are to 
do as they are intended to do, they must develop in 
themselves energy sufficient to lift them from the 
ground, and drive them forward, when required, in the 
teeth of the wind. Naturally, the first idea has been 
